Below is an example:
<a href="http://rodentia.blogspot.com/"><img src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEibo3sP8dHAdCdPBQnjx9UejLp7nxgMBef8xwsA-KelB0HStlcYqiQgveMXIwBEqe94uRTOJg3Ke6LYnpS8LRc6Z6wSemzI1ruA-tPpLY7idN38Go9nRHc-fM6S0xr_nUDfuTM6/
s400/RatsHaveRights.jpg"></a>
The "<a href=" part is the link and the "<img src=" is the photo-image-button readers will click on.
Below is the general format:
<a href="yourLink.com"><img src="yourImage.jpg"></a>
See also Links As Code